Returning from another world but as something fundamentally different.

A world where those who are summoned to another world can come back.
What would that look like do you think?
With countless forms of magic all on one planet but those who can teach it don't so to conserve their own power.
And what would happen if, a man returns with his class but is not even the same species.
What would happen if a draconic swordsman who manipulates void fire were to return from another world?